"This was a strike of choice. And it's the wrong choice for the children," Emanuel told reporters.

After five months of negotiations, "we're down to two issues," he said.

The sticking points are teacher evaluations and provisions dealing with jobs for laid-off teachers, Emanuel said.

The union, which represents nearly 30,000 teachers and support staff, called the strike on Sunday night.

The union said the two sides had been close to a deal on pay, but far apart on evaluations, benefits and other issues.

As many as 6,000 teachers could lose their jobs under the evaluation system, said union President Karen Lewis, who called the system "unacceptable."

The mayor's office, the city and school officials have questioned that job-loss figure.

The median base salary for Chicago public schools teachers in 2011 was $67,974, according to the system's annual financial report.

Some student-athletes expressed frustration after sports programs were closed.

Demetrius Harris, a senior football player at Roberto Clemente Community Academy High School, said a prolonged strike could dwindle his choices for college.

"It's really affecting our senior year," Harris told the affiliate. "I mean, we have six or seven more games left and we're trying to play as much as we can. We don't have another shot at this. It's our last year, it's our last time to prove to colleges and recruiters that we can go out and play."

Chicago teacher strike

Teacher Xian Barrett writes he knows people are angry at Chicago teachers, but the strikes is about kids, he says. Nobody wants kids in overheated classroms with too few books and more tests than teaching.

The hard-nosed stance taken by Mayor Rahm Emanuel in the Chicago teachers' strike dovetails with the education goals of his former boss, President Barack Obama, but observers disagreed Monday over how well it serves the city's schoolchildren.